It is difficult to fabricate mechanically strong and reliable small size copper electrical connections for use in oil or air cooled electrical components that are subject to high temperatures and corrosive conditions, such as rotating and stationary generator and motor components for aeronautical applications. These connections are subject to failure for reasons connected to their methods of fabrication.
For instance, in the case of a connection of a wire to an electrical connector or buss bar, a connection that comprises soldering or brazing, the heat generated by the soldering or brazing process may degrade or embrittle the wire. A connection that comprises crimping eventually degrades through the thermal cycling of the wire that loosens the seal of the crimp.
There have been some attempts to use a shape memory alloy (SMA) for fabricating electrical connectors. For instance, U.S. Pat. No. 4,022,519 to Hill describes electrical connections that comprise a resilient, non-deformable member, such as a connector pin, that deforms a non-resilient, deformable conductive member with at least a hollowed out and slotted end to accept it and a SMA force ring that surrounds the deformable conductive member proximate the inserted non-deformable member. In other words, the non-deformable member stretches and enlarges the diameter of the deformable member and the concentric SMA force ring as it penetrates the hollowed out tined end of the deformable member.
Application of sufficient heat to the SMA force ring causes the SMA force ring to shrink to its original size. Since the SMA force ring mounts concentrically on the deformable member, it deforms the deformable member around the inserted portion of the non-deformable member.
The fabricated connection of this type overcomes the disadvantages of the soldered and crimped connections described above. However, this type of connection is not suitable for all applications for several reasons. First, it requires a non-resilient, deformable member that resembles a tube to accept the non-deformable member and the SMA force ring. It is not usable if the connection requires all resilient, non-deformable materials. Second, the fabrication of this type of connection requires that the non-deforming member have sufficient strength so that it expands both the deformable member and the SMA force ring that mounts concentrically over it, or the addition of a step of expanding the deformable member and SMA force ring with a suitable mandrel. Third, the types of connections addressed by this process are only of the axial or end type, wherein the non-deformable and deformable members join in-line axially. These types of connections are not suitable for side or radial connections of wires to conductive substrates, such as buss bars, for instance.